A bridge plug can be set downhole to isolate portions of a wellbore. Some bridge plugs are retrievable from the wellbore, while others are intended to be permanently set. Retrievable bridge plugs can be set downhole using wireline, slickline, or coiled tubing and can temporarily isolate portions of the wellbore for a treatment operation or the like. Once the operation is completed, the bridge plugs can be retrieved.
As shown in FIG. 1A, a typical retrievable bridge plug 20 according to the prior art has a mandrel 22 with a wireline coupling 24, slips 26, and packing element 28. This bridge plug 20 is a Wireline Retrievable Bridge Plug (WRP bridge plug) available from Weatherford—the assignee of the present disclosure. For deployment, operators use wireline, slickline or coiled tubing (not shown) connected by a wireline or hydraulic setting tool (not shown) to the coupling 24 and deploy the bridge plug 20 to a desired point in the borehole casing (not shown). At the desired point, the plug 20 is set using the wireline or hydraulic setting tool (not shown). As the plug 20 is set, its slips 26 engage the casing, and its packing element 28 engages the casing to isolate the annulus above and below the plug 20. In general, a central portion 24a of the coupling 24 is manipulated relative to an external portion 24b so that the inner mandrel 22 moves relative to an outer sleeve 23 to compress the packing elements 28 between gage rings 29a-b and to push the slips 26 outward between wedge members (not labeled).
For retrieval, a pulling tool (not shown) is run on a tubing string downhole to the setting depth. Fluid is circulated to clear the plug 20 of debris. Once clear, the pulling tool is set down to the coupling 24 with a predetermined amount of load to shift an equalizing sleeve 25 on the plug 20. With the sleeve 25 shifted, differential pressure above and below the plug 20 equalizes so downhole pressure below the plug 20 will not force it uphole until the slips 26 and packing elements 28 are released. After equalizing the pressure differential, a predetermined amount of tension is applied by the pulling tool on the plug 20 to release the slips 26 and packing elements 28.
When used during operations, several of these retrievable bridge plugs 20 can be run in the wellbore and stacked one above another to temporarily isolate and treat multiple zones of the wellbore. When this is done, it is difficult to retrieve more than one of the bridge plugs 20 on a single run with tubing. Unfortunately, fluid cannot be circulated past the topmost bridge plug 20 to wash sand and other debris off the bridge plugs 20 disposed downhole from it in the wellbore. Without the ability to circulate fluid, it is not possible to clean debris from the lower bridge plugs 20, latch onto them, and release them in a single run. In addition, this conventional wireline-set retrievable bridge plug 20 has a tendency of resetting after being released. This resetting prevents subsequent downwards movement of the bridge plug 20, making it difficult to retrieve an uppermost plug 20 and then move it downhole without resetting before releasing a lower plug 20.
Because of the tendency of the retrievable plugs 20 to reset and the inability to circulate fluid to clear debris, operators must perform multiple trips or runs with a tubing string to retrieve all the bridge plugs 20 in the wellbore. For example, operators must circulate fluid at the topmost plug 20 to wash away debris so tubing can be coupled to the plug 20. Then, this plug 20 must be removed from the wellbore entirely so that a new run can be made to clear debris from the next lower bridge plug 20 to run it out of the wellbore. As expected, such operations can be time consuming and expensive and can expose the formation to excessive fluid losses.
To overcome the limitations of the typical retrievable bridge plug 20, Weatherford has developed another bridge plug according to the prior art for tandem retrieval. As shown in FIG. 1B, this retrievable bridge plug 30 is a modified version of the WRP bridge plug described above and has similar components. In particular, the plug 30 includes a mandrel 32, slips 36, and packing element 38 as before. Likewise, the plug 30 is set in much the same manner as before. For example, the plug 30 is run downhole, and a setting tool (not shown) coupled to the coupling 34 manipulates the central portion 34a relative to the outer portion 34b so that an inner mandrel 32 shifts relative to an outer sleeve 33 and causes the slips 36 to set and the packing element 38 to be compressed between gage rings 39a-b. 
In contrast to the previous arrangement, however, this bridge plug 30 incorporates a releasing mechanism intended to keep the plug 30 in a locked position after release. As shown, the plug 30 includes a lower extension 45 coupled to the inner mandrel 32 and extending down from the plug 30. When the mandrel 32 is shifted (uphole) during retrieval procedures of the plug 30, the extension 45 is moved up further into the plug 30, and a wedge and ring arrangement 37 on the plug 30 engages a widened and serrated portion of the extension 45 to help lock the plug 30 once released.
As also shown in FIG. 1B, a retrieval head 40 attached to a tubing string or other plug (not shown) couples to the coupling 34 at the top of the plug 30 for retrieval. The retrieval head 40 is used to equalize, release, and retrieve the plug 30 during operation. Moreover, the extension 45 has a retrieval head 40 coupled to its distal end allowing the depicted plug 30 to retrieve a lower plug in tandem. The retrieval head 40 has a collet 42 that can catch the outer portion 34b of the coupling 34 and has an outer sleeve 44 that can open the equalizing sleeve 35 at the top of the plug 30.
As noted above, the plug 30's releasing mechanism helps keep the plug 30 in a locked position after release. Combined with the extension 45 and retrieval head 40, the plug 30 has been used in operations where several such plugs 30 have been retrieved in tandem. However, the plug 30 still fails to adequately address circulating fluid down to the next plug to clear it of debris for tandem retrieval. Although fluid may find its way past the plug 30 during retrieval operations so that fluid can clear some debris away from the lower plug 30, a great deal of fluid may be lost in the process. Therefore, more fluid is lost to the formation during retrieval. Moreover, additional amounts of fluid are required to clear debris from even lower plugs and can result in undesirable loss of fluid to the formation.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.